docs: def merge_all_models_into_first_model(biop_structure):
      """Merge all existing models into a Structure's first_model attribute.
  
      This directly modifies the Biopython Structure object. Chains IDs will start from A and increment for each new
      chain (model that is converted).
  
      Args:
          biop_structure (Structure): Structure with multiple models that should be merged
  
      """
      from string import ascii_uppercase
      idx = 1
      first_model = biop_structure[0]
  
      for m in biop_structure.get_models():
          # Don't duplicate the original model
          if first_model.id == m.id:
              continue
          for c in m.get_chains():
              c.id = ascii_uppercase[idx]
              first_model.add(c)
          idx += 1